Armor Unit

ABSTRACT

Armor units for rubble mound structures including breakwaters, revetments, groins, jetties, and the like. Embodiments are appropriate for ocean, river, lake and reservoir structure armoring, to prevent erosion from damaging hydrodynamic forces resulting from waves and water currents, and the like. An embodiment includes a central rectangular section, three “half H-shaped” appendages, two identical frusta (end members), and a flat bottom with two extrusions, nominally smaller than other appendages and frusta. An embodiment is symmetric about two perpendicularly intersecting vertical planes extending through the centroid of the unit. The three half H-shaped members are connected to outer parts of a side defined as the top and the two longitudinal sides of the central section. The three half H-shaped members and the two end members comprise four-sided frusta that taper from a base at the central rectangular section to four-sided distal ends. For select embodiments, the frusta are generally symmetric.

RELATED APPLICATIONS

This application is a national phase application, filed as a national stage under U.S.C. § 371, of International Application No. PCT/U.S. 08/52,146, filed Jan. 28, 2008, which claims the benefit Under 35 U.S.0 .§ 119(e)(1) of prior co-pending U.S. Provisional Patent Application Ser. No. 60/898,412, Concrete Armor Unit, by Melby et al., filed Jan. 31, 2007, both incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

Under paragraph 1(a) of Executive Order 10096, the conditions under which this invention was made entitle the Government of the United States, as represented by the Secretary of the Army, to an undivided interest therein on any patent granted thereon by the United States.

This and related patents are available for licensing to qualified licensees. Please contact Phillip Stewart at 601 634-4113.

BACKGROUND

Breakwaters are generally shore-parallel structures that reduce the amount of wave energy reaching the protected area. They are similar to natural bars, reefs or near shore islands and are designed to dissipate wave energy. For breakwaters protecting harbors, the breakwater acts as a barrier to wave energy and often to direct alongshore sediment transport away from the harbor. For shore protection, offshore breakwaters provide a reduction in wave energy in the lee of the structure slowing the littoral drift, producing sediment deposition and a shoreline bulge or “salient” feature in the sheltered area behind the breakwater. Some alongshore sediment transport may continue along the coast behind a near shore breakwater.

There are various types of breakwaters. These include:

Headland breakwaters, a series of breakwaters constructed in an “attached” fashion to the shoreline and angled in the direction of predominant wave approach such that the shoreline behind the features evolves into a natural “crenulate” or log spiral embayment.

Detached breakwaters that are constructed away from the shoreline, usually a slight distance offshore. They are detached from the shoreline, and are designed to promote beach deposition on their leeside.

Single breakwaters that may be attached or detached depending on what they are being designed to protect. A single detached breakwater may protect a small section of shoreline. A single attached breakwater, may be a long structure designed to shelter marinas or harbors from wave action.

System breakwaters refer to two or more detached, offshore breakwaters constructed along an extensive length of shoreline.

Rubble mound jetties are often referred to as breakwaters. They are oriented shore-perpendicular and usually built as a pair at a natural inlet, to provide extension of a navigation channel some distance from the natural shoreline. These structures redirect the sediment transport away from the navigation channel and constrain the tidal flow in the channel in order to make an efficient channel that requires little maintenance for navigation compared to a natural inlet.

Breakwaters are typically constructed in high wave energy environments using large armor stone, or pre-cast concrete units or blocks. In lower wave-energy environments, grout-filled fabric bags, gabions and other proprietary units have been utilized. Typical breakwater design is similar to that of a revetment, with a core or filter layer of smaller stone, overlain by the armoring layer of armor stone or pre-cast concrete units.

Armor units conventionally constructed of concrete are typically used to protect rubble mound structures in relatively high wave environments or where stone armor is not readily available. Rubble mound structures include breakwaters, revetments, jetties, caissons, groins and the like. Coastal rubble mounds are gravity structures. Conventional armor units are heavy in order to prevent displacement or rocking from waves and currents.

Armor units are typically displaced by one or both of two dominant modes of structure failure. The first is displacement of the armor which leads to exposure and erosion of filter layers and subsequently the core. The second is armor breakage. The breakwater or revetment capacity will be significantly reduced if either of these two failure modes occurs and progressive failure of the structure made much more likely. The under layer (filter layer) is sized so as to not move under undamaged armor and to prevent interior stone (e.g., small quarry-run stone) from escaping.

A wave is described by its height, length, and the nature of breaking. The wave height is the dominant forcing parameter considered in designing armor units. Other parameters include wave length, water depth, structure shape and height, armor layer porosity, degree of armor interlocking, inter-unit friction, and armor density relative to the water.

It is known that waves exert forces on armor units in all directions. Slender armor units usually require steel reinforcement while more stout armor shapes do not. Adequate steel (rebar) reinforcement increases material costs by roughly 100% over un-reinforced concrete. Both steel and polypropylene fiber reinforcement have been used to provide about 10-20% increase in flexural tensile strengths for large armor. units. The cost increase for the fiber-reinforced concrete equates to an equivalent percent increase in strength.

Existing concrete armor units are described in the U.S. Army Corps of Engineers design manuals Coastal Engineering Manual and the Shore Protection Manual. See, e.g., http://chl.erdc.usace.army.mil/chi.aspx?p=s&a=ARTICLES;104). Popular armor units include dolos, tribar, CORE-LOC®, ACCROPODE®, tetrapod, SAMOA STONE™, Antifer cube, concrete cube, shed and cob. The CORE-LOC® armor unit is protected by U.S. Pat. Nos. 5,441,362 and 5,620,280, each to Melby et al., and each incorporated herein by reference.

Commonly used concrete armor units have features that are advantageous for certain applications but are not suitable for other applications. Advantages include:

-   -   Highly porous so good wave dissipation (CORE-LOC®, ACCROPODE®,         tetrapod, dolos, random cube, shed, cob, tribar)     -   Good interlocking in all directions (dolos, CORE-LOC®, tetrapod,         Samoa Stone™)     -   Good structural capacity (small to medium sized CORE-LOC® and         ACCROPODE®, tetrapod, cube, Samoa Stone™)     -   Armor layer can deform without catastrophic failure (random         cube)     -   Simple mould construction (cube)     -   Simple armor unit to cast (cube, Samoa Stone™)     -   Simple armor unit to place (cube, Samoa Stone™)

Disadvantages include:

-   -   Poor interlocking (cube, tetrapod, other armor if not correctly         placed)     -   Marginal structural capacity (very large CORE-LOC and         ACCROPODE®, large tribar, dolos, shed, cob)     -   Structure is brittle and fails abruptly (most concrete armor         layers)     -   Relatively complex mould construction (CORE-LOC®, tribar, dolos,         shed, cob, ACCROPODE®)     -   Relatively difficult armor unit to cast (CORE-LOC®, tribar,         dolos, shed, cob, ACCROPODE®)     -   Difficult armor unit to place in low visibility or moderate         background waves (CORE-LOC®, tribar, dolos, shed, cob,         ACCROPODE®)     -   Relatively large under layer required because pore spaces are         large (CORE-LOC®, tribar, dolos, ACCROPODE®)

For most armor units, it is difficult to achieve adequate interlocking when placing underwater. This is particularly true when the visibility is low and there are background waves during construction. For pattern-placed armor, it is virtually impossible to place them correctly with no visibility or when background waves are present. This condition is quite common.

Many armor units require a relatively smooth under layer (CORE-LOC®, ACCROPODE®, tribar, shed, cob, cubes if pattern-placed). Achieving interlocking and a smooth under layer when there is low visibility and background waves is extremely difficult and the uncertainty has led to cost overruns and even breakwater failures.

Relatively slender armor units, such as dolos, CORE-LOC®, ACCROPODE®, tribar, and hollow blocks like the shed and cob, require high-cost moulds and are challenging to cast. Metal mould cost depends on the number of plates and complexity of the bends. Some armor unit moulds require 75-100 plates. Cubes require the fewest plates but have all the concrete concentrated in one mass. This produces high heat of hydration and potential thermal cracking. Tall moulds used for large dolos, CORE-LOC®, ACCROPODE®, and hollow blocks also have potential for significant strength variations throughout the armor unit because the aggregate settles, compaction is greater at the bottom of the mould, and water rises when the concrete is vibrated during casting. High water-to-cement ratios and over-vibration, which can occur in poorly supervised construction, results in degraded armor units. For example, aggregate can concentrate in the lower portion of the unit while the upper portion has an abnormally high water-to-cement ratio yielding weaker concrete. In addition, complex shapes have horizontal or shallow sloping surfaces where water can pool in the mould, further reducing strength. The result is that tall complex shapes depend greatly on the quality of construction processes and can yield less than optimum strength.

The application dictates the appropriate armor unit. For shallow, clear water with insignificant background wave conditions, and waves under eight meters in height, most of the previously discussed armor units can be constructed and placed without difficulty. In these cases, an engineer chooses the least expensive unit that provides the prescribed reliability. However, for low visibility, high background wave conditions, or waves of eight meters or greater, the disadvantages of inexpensive existing armor units mean that construction of a quality structure is going to be difficult and expensive and may even be filled with uncertainty. Further, long slopes in armored configurations provide more opportunity for down-slope settlement and potential armor breakage or displacement as the interlocking is lost. Although cube armor units are relatively easy to construct, they do not interlock so maintenance costs are much higher than other designs and cube armor requires far more concrete than many other designs.

Interlocking concrete armor units or erosion prevention modules are well-known in the patented prior art as evidenced by the Kaneko et al., U.S. Pat. No. 3,614,866 and Chevallier, U.S. Pat. No. 4,347,017.

The Kaneko et al. patent discloses a polypod block comprised of at least three integral pillar-shaped parts joined in an alternately crossed relationship. Hence, the block has at least six appendages which interlock with other blocks so that a large number of blocks can be arranged to form tightly assembled combinations. The pillar-shaped members are joined together with a minimum amount of shared surface area yielding significant stress-concentrations at joints. Because of this, the configuration has a high probability of breaking individual units, potentially leading to massive failure of the configuration. Further, the appendages do not stay connected because the pillar-shaped members have a square cross-section that provides a limited area of frictional engagement with neighboring blocks. Because of the regular arrangement of the individual units, catastrophic failure of the installed configuration can result from the failure of a relatively few armor units. Finally, regularly placed units of the configuration produce an armor layer with very low porosity, providing little wave energy dissipation and therefore little contribution to reduction in wave energy for the protected area in the lee of the configuration.

The Chevallier patent discloses an armor unit, commonly known as the ACCROPODE®, for protecting riverside structures and shorelines. The unit comprises a cubic central core having top and bottom surfaces provided with anvil-shaped legs and opposed front and rear legs in the form of four-sided truncated pyramids. Hydraulic stability characteristics of the Chevallier unit are good if the units are well interlocked but marginal if not because of the anvil-shaped legs that provide minimal unit-to-unit wedging. The units rely primarily on gravity forces from overlying units to enhance individual unit stability. Therefore these units must be placed on steep slopes to assure stability. However, steep-sloped structures have a tendency to fail catastrophically and have proven to have a high probability of failure and risk when used in low-visibility waters, in deep water, or when construction is done in relatively high wave environments. Placed on slope, a Chevallier unit exhibits characteristics of a low-porosity armor layer due to the fact that it is placed in a single layer. This provides less reduction in wave energy than found in an armor layer composed of multiple layers of more slender armor units. Further, the Chevallier blocks require fairly severe constraints and specifications for placement on the breakwater in order to develop enhanced hydraulic stability.

Practical difficulties result in the manufacture, storage and transport of armor units. For example, some armor units have shapes which are not easily cast or formed. For example, the units of Yang, U.S. Pat. No. 6,666,620 B2 contain complex leg formations (“a cylindrical body, tapered lump legs projecting from the cylindrical body and branch legs cylindrically projected through a circular base disposed on the cylindrical body”). Some armor units, such as the Yang units, do not allow for nested placement in yard areas or in shipping barges, and consequently are difficult to store and ship efficiently. Also, some structures are not repairable by simple addition of replacement armor units, but must be partially disassembled. For example, the units of Detiveaux, U.S. Pat. No. 6,361,247 B1 require insertion of a long spike section into the earth and stabilization of the section with guide wires. The amount of wave dissipation is minimal provided through small windows in the top of the structure.

The designs of Melby et al. addressed many inherent weaknesses of the above designs but provided little improvement over existing shapes in fabrication, requiring skilled supervision in casting the final product, as well as for emplacement of individual units where poor visibility or moderate to severe wave action exists.

Concrete armor units are shaped to provide improved performance over stone as armor. The unit's shape may include appendages to promote interlocking between neighboring units. Hundreds of shapes have been developed, however, relatively few shapes are used as noted in the abbreviated list above. Many shapes are either too slender, thus prone to breaking, or provide resistance to wave forces in only a single plane, e.g., Detiveaux.

There is thus a need for a durable interlocking armor unit capable of random placement resulting in a stable configuration that has strong individual units while being relatively straightforward to fabricate. Each unit should have slender appendages to provide improved stability and wave energy dissipation yet be strong enough to prevent failure of any single unit. The unit should be suitable for repair of existing slopes. It should be relatively simple to fabricate and lend itself to ready stacking for storage and shipping, thus reducing overall cost, as well as to emplacement in conditions not conducive to emplacing existing units.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a select embodiment of the present invention.

FIG. 2A is a perspective view from the top of a select embodiment of the present invention.

FIG. 2B is a perspective view from the bottom of a select embodiment of the present invention.

FIG. 3 is a view looking at the bottom of a select embodiment of the present invention.

FIG. 4 is a view looking at the longest side of a select embodiment of the present invention.

FIG. 5 is a head-on end view of a select embodiment of the present invention, looking down the longest axis.

FIG. 6 is a top view of a single layer interlocking configuration of the embodiments of FIG. 1 as may be installed on a breakwater.

FIG. 7 is a top view of a multi-layer interlocking configuration of the embodiments of FIG. 1 as may be installed on a breakwater.

FIG. 8 is a top view of a random multi-layer interlocking configuration of the embodiments of FIG. 1 as may be installed on a breakwater.

FIG. 9A is an end view of a select embodiment of the present invention that is similar to the embodiment as shown in FIG. 5, differing only in that the end frusta terminate in an integral chisel shape.

FIG. 9B is a perspective view of the chisel shape of the ends of the end frustum in FIG. 9A.

FIG. 10 is a top view of a configuration of the embodiments of FIG. 1 in which all but the bottom row are arranged with the bottom of the embodiment of FIG. 1 as one of the sides.

DETAILED DESCRIPTION

Select embodiments of the present invention envision a concrete armor unit for armoring alongshore structures of rivers, lakes, and reservoir banks; coastal shorelines and coastal revetments; and rubble mound breakwaters, jetties, caissons and groins to prevent erosion from damaging hydrodynamic forces of waves and water currents. The armor unit may also have application to dam spillway and riverine baffle systems required to slow hydraulic flow. Select embodiments of the present invention provide an armor unit (erosion prevention module) that is uniquely configured to produce a high degree of interlocking while providing stability on steep as well as relatively shallow slopes on which it may be installed. Refer to FIG. 2A providing a perspective including a top surface 201 and FIG. 2B providing a perspective including a bottom surface 202 of a select embodiment of the present invention. The module has appendages 102, 103, 106 that provide hydraulic stability and wave energy dissipation. Internal stress levels are minimized by filleting 105 between the intersections of the two appendages 103 on each of three long sides and by providing extrusions (“supports”) 106 on the fourth (bottom) side.

Refer to FIG. 1. Select embodiments of the present invention may comprise: a central rectangular section 101 with central elongate axis and three “artistic” half H-shaped members 103 (the “H” bisected top to bottom through the intersection horizontal bar to create half of an “H”) extending from each of three of the four elongate sides of the central rectangular section 101 such that each half H-shaped member 103 along the sides has an upper surface formed by four sides of each of the vertical parts of the half “H” sloping away from the central axis of the rectangular section 101 and parallel to a bottom surface of the half “H” in the same plane as the appropriate side surface of the central rectangular section 101. The vertical portions of each half H-shaped member taper uniformly and symmetrically about the central axis, such that each half H-shaped member is composed of two identical outer frusta 103 connected in the center by a fillet (wedge) 105. Each frustum 103, 105 has a rectangular cross-section at its base and a smaller rectangular cross-section at its distal end 104 due to the tapering of the four sides of the frustum 103 away from its base. End frusta 102 are positioned on each of the ends of the rectangular section 101, with a longitudinal central axis coincident with the longitudinal central axis of the rectangular section 101. End frusta 102 may have a similar cross section to the frusta 103 associated with the half H-shaped members such that each end frustum has a rectangular flat bottom surface coincident with the bottom surface of the end of the rectangular section 101. To complete the armor unit, two or more extrusions 106 (FIG. 2B) may extend vertically downward from the rectangular central section and may be of the same shape as either the end frusta 102, the half H-shaped member frusta 103, or both. The half H-shaped member frusta 103 are separated by a fillet (wedge) 105 establishing a distance equal to or slightly greater than the dimension of the half H-shaped member frustum 103 at the outer surface of the fillet 105. This geometry facilitates interlocking between neighboring armor units, such that the armor unit is symmetric about a vertical plane extending through the centroid parallel to the longitudinal central elongate axis of the rectangular section 101 and such that the armor unit is symmetric about a vertical plane extending through the centroid and perpendicular to the central elongate axis. In select embodiments of the present invention the half H-shaped members are equal in height, d (FIG. 1).

Note that setting the thickness of the rectangular section 101 equal to the width (thickness and width defining the dimensions of the end of the rectangular section 101) creates square bases for the end frusta 102 and if the length of the rectangular section 101 is equal to twice the width, all frusta 102, 103 may be of the same shape at the base. If the angle of slope, α (FIG. 1) is held constant for all four faces of each frusta 102, 103, the frusta are the same shape overall. Finally, if the height, d, of each of the frusta 102, 103 is also identical, all frusta 102, 103 are identical having square bases and distal end faces that are square.

Select embodiments of the present invention provide armor units as the fundamental component for protecting ocean, coastal, river, lake and reservoir banks, and base structure layers from the damaging hydrodynamic forces of waves and water currents. Refer to FIG. 1. In select embodiments of the present invention, an armor unit includes a central rectangular section 101 having a length, 2L, longer than its width, L, and a depth equal to (see L at FIG. 4) or shorter than its width. Each of three of the long sides of the rectangular section (box) 101 include two outer members that are frusta 103 whose four-sided bases are each defined by one-half of the perimeter of the long side of the central rectangular section 101 and a line bisecting the longitudinal axis of the central rectangular section 101. In select embodiments of the present invention, a fillet 105 in the center of each of the three long sides effectively shortens the “internal” side 107 of each of the frusta 103 on these three long sides. On each of the two ends (short sides) of the central rectangular section 101 is a single frustum 102 whose four-sided base is defined by the width and depth of the central rectangular section 101. Width and depth are shown as equal if FIGS. 3 and 4 are taken to be of the same armor unit, but need not be. The remaining long side (bottom) 202 in FIG. 2B has two frusta 106 incorporated as “supports” and thus this fourth long side defines the bottom surface 202 of the armor unit, established for ease of fabrication of the armor unit as well as for the utility of it. These supports 106 may be frusta of the same general shape as that of the other three sides, the ends, or both, and may be centered in the same location on the fourth long side (bottom) 202 as those frusta on the opposing (top) 201 side. In select embodiments of the present invention, the four-sided base of these two supports (frusta) 106 has a smaller perimeter and the height, d, of these two frusta 106 is shorter than those of the frusta 103 on the other three long sides. This design promotes a high degree of wedging while providing many paths for wave dissipation over the surfaces of the appendages 102, 103, 106 of the armor unit.

Select embodiments of the present invention may incorporate internal reinforcing bars or “rebar.” A suitable reinforcement may be that described in U.S. patent application Ser. No. 11/234,184, to Day et al., incorporated herein by reference. Select embodiments of the present invention were developed to provide optimized armor units for situations when conditions are not ideal for casting or placing concrete armor units, or both. Select embodiments of the present invention are designed to be stout, simple to cast, and easy to place in adverse conditions on a breakwater, revetment, or jetty. Refer to FIGS. 2A and 2B. For select embodiments of the present invention, the shape resembles a stout crocodile with short nose 102 and tail 102, four short legs 103 on the sides, and two back ridges 103, hence the name C-ROC®. In select embodiments of the present invention, the bottom (“belly”) 202 is flat except for two or more short extrusions 106.

For select embodiments of the present invention, the moulds are less expensive to fabricate than conventional armor units because the number of plates is less. For select embodiments of the present invention the mould has only 33 flat plates in its primary configuration, i.e., without the belly extrusions 106. This is one of the lowest plate numbers of known complex-shaped interlocking units. Further, since all plates are flat the mould is relatively easy and inexpensive to construct.

For select embodiments of the present invention, casting is simple because the vertical height of appendages 102, 103, 106 in any direction is shorter than conventional armor units. In select embodiments of the present invention the casting mould is open on the bottom allowing the armor unit to be cast on a slab with holes (not shown separately) for belly extrusions 106. Thus, select embodiments of the present invention have a low center of gravity (cg) during casting. This low cg limits water pooling and aggregate movement while needing only minimal vibration to insure the integrity of the casting. Further, with the broad center of the unit's mass directly supported by a casting slab, there are little, if any, tensile stresses developed during casting.

The shape of select embodiments of the present invention is not as slender in select dimensions as any of the dolos, CORE-LOC®, ACCROPODE®, or hollow blocks like the shed and cob. Typical embodiments of the present invention require 38% more material than an equivalent CORE-LOC® armor layer, 27% more material than an ACCROPODE® armor layer, and 20% less material than an armor layer made with dolos armor units.

Select embodiments of the present invention are constructed such that each armor unit is placed with its longitudinal axis roughly perpendicular to the slope of the breakwater or revetment, i.e., roughly horizontally on the slope. This results in spacing between select embodiments of the present invention being less than for most large conventional armor units.

This configuration reduces or prevents movement of the under layer. In addition, placement on a breakwater or revetment is simple and can be done in low visibility conditions or with moderate background wave conditions. It is expected that divers with specialized skills would not be required since straightforward techniques are used for emplacement.

Hydraulic stability tests of select embodiments of the present invention demonstrate that these embodiments are very stable when placed on a typical breakwater cross section at a slope of 1V:2H. The Hudson stability equation is used to design armor units for a given incident wave height, a given stability coefficient and breakwater slope. The equation is given by

$\begin{matrix} {\mspace{20mu} {W = \frac{\gamma_{r}H^{3}}{{K_{D}\left( {S_{r} - 1} \right)}^{3}\cot \; \alpha}}} & (1) \end{matrix}$

where:

-   -   W=mean weight of an armor unit,     -   γ_(r) =unit weight density of material comprising armor unit,     -   H=design incident wave height near the structure (breakwater or         revetment),     -   K_(D)=empirical stability coefficient describing the effect of         parameters (e.g., breaking waves) that are not individually         identified,     -   S_(r)=specific gravity of armor unit material relative to water         that the structure is in, and     -   cot α=seaward structure slope.

K_(D) describes, in part, the degree of interlocking of the unit. The higher the K_(D), the higher the stability. For example, stone exposed to breaking waves has a K_(D)=2 give the condition of 5% eroded volume for the stone. Early tests of dolos, CORE-LOC® and ACCROPODE® indicated a K_(D) greater than 50 with little or no measurable damage. The values recommended for design are K_(D)=8-16 for dolos, K_(D)=12-16 for CORE-LOC® and K_(D)=10-13 for ACCROPODE®.

The unit weight density, γ_(r), of the material selected for the armor unit is an important factor in attaining both an optimum weight and toughness of the armor unit. One such material is an improved high strength concrete as described in U.S. patent application Ser. No. 11/390,084 to O'Neil et al., incorporated herein by reference.

The CORE-LOC® armor unit is regarded as the most stable of commonly used armor units. Tests of select embodiments of the present invention yielded a K_(D) of 61 with no instability on the seaward slope, indicating these embodiments have stability characteristics comparable to the best shapes available. Because select embodiments of the present invention are not fragile as are more slender armor units, reliability of select embodiments of the present invention is greater.

In select embodiments of the present invention the armor unit comprises in large part portland cement-based concrete.

For select embodiments of the present invention, the uniform tapering of the half H-shaped members facilitates wedging of adjacent armor units when placed in a layer on a rubble mound. The uniform taper also aids in removal of the mould during fabrication. For select embodiments of the present invention the flat bottom surface facilitates casting and the added extrusions insure bottom surface roughness and interlocking when the armor unit is installed.

EXAMPLE

Refer to FIG. 1 depicting a top view of a select embodiment 100 of the present invention. This view also shows the position of two “extrusions” (supports) 106 (dotted lines) on the bottom of the armor unit relative to the two vertical portions (frusta) 103 of the half H-shaped member on the top of the armor unit.

In this example, the length of the central rectangular section is 2L, the width is L, and the depth is L. Thus, each of the frusta 102, 103 have square bases of the same dimension, lending to the overall symmetry of the armor unit. Note that the two frusta 103 on each of three longitudinal sides have a square base of L×L, just as the end frusta 102 do (see FIG. 4 for a side view confirming a thickness of L). If the fillet 105 were not employed, one could readily observe that the two side frusta 103 touch at the center of the long side of the central rectangular section 101. As to the fillet 105, the width, v, is defined by selecting the depth, t, of the fillet 105. Similarly, the dimension, w, of the square top surface of each frusta 102, 103 is defined by selecting the height, d, with the taper having been previously specified by the angle a.

In select embodiments of the present invention, to optimize symmetry of the armor unit, the angle of taper, α, is maintained the same for at least the frusta 103 of the three sides with half H-shaped members and the frusta 102 of the two ends. This angle may even be maintained for the two or more extrusions 106 as shown in FIG. 4.

Refer to FIGS. 3 and 4, depicting a view of the bottom and side, respectively, of the armor unit of FIG. 1. As can be seen in this embodiment, each extrusion 106 is “centered” on a vertical line through the armor unit that passes through the middle of a corresponding frusta 103 on the top side. The slope of the short frusta comprising an extrusion 106 may be set equal to that of the other frusta 102, 103, i.e., set at α. Given α and the dimension, x, of the side of the base of the extrusion 106, the space, s, between the extrusions 106 is defined. Further, given the dimension, u, of the side of the top surface of the extrusion 106 (the surface on which the armor unit would sit as shown in FIG. 4), the height, γ, of the extrusion is defined.

Refer to FIG. 5, a “head-on” end view of the embodiment of FIG. 1. In this view, the symmetry is apparent when the thickness of the central rectangular section 101 is chosen to be equal to the width of the central rectangular section 101. Given the 2:1 relationship of length to width and selection of a common taper pre-specified as a as shown in FIG. 1, each of the three illustrated “side” frusta 103 are identical in base area to the end frusta 102. If the height, d, is common to both the end 102 and side 103 frusta, then the 6 side frusta 103 and two end frusta 102 extend equidistant from the central rectangular section 101 and provide the same cross section 104 at their respective distal ends.

Refer to FIGS. 2A and 2B. The thickness of the central rectangular section 101 need not be the same as the width. With a thickness less than the width, an embodiment would be as presented in FIGS. 2A and 2B, exhibiting a rectangular face 104 at the distal end of each of the frusta 102, 103 and possibly that of the extrusions 106 if symmetry with the top side frusta 103 is desired.

Refer to FIG. 6, an interlocking single layer configuration 600 of the individual armor units 100 as shown in FIG. 1. The individual units 100 are arranged with longitudinal axes horizontally along the slope of the breakwater. This provides a series of zigzag horizontal lines of armor units each interlocked with an armor unit in the lines above and below it and each having end frusta abutting along their slope with end frusta of adjacent units in the, horizontal line.

Refer to FIG. 7, an interlocking multi-layer configuration 700 of the individual armor units 100 as shown in FIG. 1. The individual units 100 are arranged in two layers with longitudinal axes oriented horizontally along the slope of the breakwater. The multi-layer configuration covers the gaps present in the single layer configuration of FIG. 6, albeit at a greater expense for the same size armor units 100.

Although FIG. 7 shows alignment of the armor units 100 horizontally in a precise interlocking order over the slope of the breakwater, armor units 100 may be randomly placed in one or multi-layers with orientation of the unit's longitudinal axis with respect to the slope of the breakwater up to 45° from horizontal. See FIG. 8 in which each unit in a bottom layer is arranged higgledy-piggledy with respect to its neighbors and overlaid with a top layer arranged in the same manner. It is evident that there is still available a considerable amount of interlocking and full coverage of the under layer of the breakwater even in a pseudo-random or random orientation of the armor units 100 when arranged in multiple layers.

Refer to FIG. 9A, an end view of an embodiment 900 similar to the embodiment 100 as shown in end view in FIG. 5, except for termination in a blunt 902 chisel shape 901 at the distal end of each end frustum 102. These chisel-shaped terminations 901 may be provided to improve ease of removal of an embodiment from a casting form or for enhancing the integrity of the distal ends of embodiments, or both. FIG. 9B is a perspective of the blunt 902 chisel-shaped termination 901 alone. In one an embodiment of the present invention this configuration adds length to each of the end frusta 102 represented in FIG. 1 as embodiment 100 if the same size frusta are used for the end frusta 102 as for the side frusta 103 prior to incorporating the integral blunt 902 chisel-shaped termination 901. If the angle β is kept small, e.g., less than about 10° and preferably about 5°, then the additional mass added to the end frusta 102 is minimized, while the ease of removing a casting form is optimized.

Refer to FIG. 10. A first row of armor units may be placed on a sloping breakwater at the toe of the slope in much the same manner as shown in FIG. 6, i.e., in a single plane with the “bottom” (side with the extrusions 106) placed adjacent the understructure. Second and succeeding rows may be arranged such that the longitudinal axis is roughly perpendicular to the slope and a “side” (side with the frusta 103) is placed adjacent to a neighboring unit such that the rotation about the longitudinal axis is random as shown in the second, third and fourth rows of FIG. 10. Some units may be placed with the bottom turned 90° (i.e., as one side of the emplaced armor unit) as shown in the second, third and fourth rows of FIG. 10 so that the bottom of an armor unit need not always face down. Further, the individual units need not be in the same plane, i.e., they may overlap with other units in the same or adjacent rows making the row taller where overlap occurs and shorter where the unit angles down on an opposite side as a result of the overlap. This configuration of armor units is suited to steeper slopes and those where high or murky water limits the visibility that would permit a “structured” interlocking of armor units as shown in FIGS. 6 and 7. Note also that although FIG. 10 does not employ units with the chisel-shaped end caps 901 of FIG. 9, the embodiment of FIG. 9 may be used in the breakwater of FIG. 10 or any other breakwater, including those comprising completely random placement of one or multiple layers of armor units.

The abstract of the disclosure is provided to comply with the rules requiring an abstract that will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. 37 CFR § 1.72(b). Any advantages and benefits described may not apply to all embodiments of the invention.

While the invention has been described in terms of some of its embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims. For example, although the system is described in specific examples for providing a suitable armor unit having symmetry on at least three sides, other alternatives are possible, to include selection of different slope angles, α, for one or more sides, different heights, d, for one or more sides, a different number and type of extrusions 106, and the like. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. Thus, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting, and the invention should be defined only in accordance with the following claims and their equivalents. 

1. An armor unit for stabilizing rubble mound structures such as coastal revetments, breakwaters, and the like, comprising: a central configuration having a longitudinal axis, a first pair of sides parallel one to another and to said longitudinal axis, a second pair of sides parallel one to another and to said longitudinal axis and perpendicular to said first pair of sides; and a pair of ends, one proximal and the other distal with respect to said longitudinal axis, said ends parallel one to another and perpendicular to said longitudinal axis and to each of said first and second pairs of sides; and first right frusta, each said first right frusta having a proximal base coincident with said side on which said first right frustum is located and a distal base, said distal base defined by an angle, α, the angle of uniform taper of each said side of said first right frustum from said central configuration and a height, d, of said first right frustum, wherein, one said first right frustum is coincident with each said end and at least two each said first right frusta are coincident with each said side on at least three of said four sides; and wherein, said uniform taper facilitates wedging of adjacent armor units when installed in an array, and wherein said uniform taper facilitates removal of the mold for casting said armor unit, and wherein said first right frusta provide hydraulic stability and wave energy dissipation, and fillets, one each of depth, t, incorporated between each said two first right frusta incorporated on said at least three sides, t<d, wherein, said fillets minimize internal stress levels of said armor unit, and wherein, the degree of interlocking of said armor unit one to another, as described by the two dimensional stability coefficient, K_(D), is greater than about
 50. 2. The armor unit of claim 1 in which said first right frusta are incorporated in pairs on three said sides, each said side equal in area, and each said first right frusta of equal height and each said proximal base of said first right frusta equal to one-half of the area of each said side such that the complete area of each said three sides is covered by said first right frusta, and in which said proximal base of said first right frusta incorporated in said ends cover the complete area of each said end, and in which said fourth side incorporates at least two extrusions, wherein said fourth side comprises the bottom of said armor unit in one application thereof, and wherein, said extrusions provide bottom surface roughness and facilitate interlocking of said armor units when installed in an array.
 3. The armor unit of claim 2 in which said extrusions are in the form of at least two second right frusta, each second right frustum smaller in at least one dimension than any said first right frustum.
 4. The armor unit of claim 3 in which all said second right frusta are equal one to another in each dimension and angle of inclination.
 5. The armor unit of claim 2 in which said first right frusta are cast integrally with said central configuration and said extrusions are cast separately from said first right frusta and said central configuration, wherein said separate casting permits a main portion of said armor unit to be cast on a flat surface thereby reducing internal stress on said armor unit.
 6. The armor unit of claim 1 in which said all first right frusta are equal one to another in each dimension and angle of inclination.
 7. The armor unit of claim 1 in which said first right frusta incorporated in said ends terminate in a chisel shape such that said distal base of said first right frusta incorporated in said ends is terminated with two opposing sides of said frusta at an angle, β, with respect to said bases, said angle β less than said angle α.
 8. The armor unit of claim 7 in which said angle β is less than about 10°.
 9. The armor unit of claim 1 comprising at least in part concrete.
 10. The armor unit of claim 9 in which said concrete is concrete conventionally described as very high strength concrete (VHSC).
 11. The armor unit of claim 1, comprising at least in part reinforcement.
 12. The armor unit of claim 11 in which said reinforcement comprises metal.
 13. The armor unit of claim 11 in which said reinforcement comprises coated metal, wherein said coating improves bonding strength of said reinforcement to said concrete.
 14. The armor unit of claim 1 in which said bases are squares.
 15. An array of said armor units of claim 1 dispersed so as to wedge said armor units against other said armor units thereby stabilizing breakwaters of varying slopes, wherein, said array is constructed such that each said armor unit is placed in close proximity to at least one other said armor unit such that said array reduces or prevents movement of an under layer, and wherein, placement of said armor units on a breakwater can be done in low visibility conditions and with moderate background wave conditions.
 16. The array of claim 15 in which said longitudinal axis of each said armor unit is placed approximately perpendicular to the slope of said breakwater.
 17. An inexpensive mold for casting said armor unit of claim 1, said mold comprising a plurality of flat panels, said mold further open at the bottom for subsequent addition of said extrusions, wherein said mold has a have a low center of gravity during casting that limits water pooling and aggregate movement, and wherein said mold requires only minimal vibration to insure the integrity of said armor unit.
 18. The mold of claim 17 comprising 33 flat panels.
 19. A method of stabilizing a breakwater comprising: interlocking a single layer array of armor units of claim 1, arranging said longitudinal axes of each said armor unit perpendicular to the slope of said breakwater, wherein said interlocking results in a series of zigzag horizontal lines of said armor units each said line interlocked with a said armor unit in said lines above and below and each having end frusta abutting along said slope with end frusta of adjacent units in each said horizontal line.
 20. The method of claim 19 further comprising interlocking said armor units arranged in two layers with said longitudinal axis of each said armor unit oriented perpendicular to said slope of said breakwater.
 21. A method of stabilizing a breakwater comprising randomly placing armor units of claim 1 with orientation of said longitudinal axis of each said armor unit with respect to said slope of said breakwater arranged as much as about 45° from perpendicular to said slope.
 22. An armor unit incorporating right frusta, each said frustum of approximately the same shape and dimension as other said frusta, said frusta arranged on a central core of said armor unit, said central core having surfaces on six sides, said surfaces including a top, a bottom and two side surfaces, each of said top, bottom and two sides parallel to a longitudinal axis of said central core, and first and second end surfaces perpendicular to said longitudinal axis, said end surfaces defining the length of said central core, at least one said frustum incorporated on each of at least five of said six sides and one said frustum incorporated in each of said ends. 